There is an old adage, “rice harvest is good in a year with lots of thunder”. It is said to be caused by the fact that thunder produces nitrogen oxide in the air. Previously, several technologies have been disclosed to apply electrical treatment to plants in order to accelerate plant growth.
In Patent Literature 1, technology is disclosed, which accelerates growth of mushrooms by giving spark discharge to the mushroom cultivation body that was cultivated from mushroom mycelium. Since the technology generating spark discharge as in Patent Literature 1 causes risks to workers with the spark discharge, not only the target plants are limited but also the growth environment is restricted, and an issue arose that the technology cannot be applied to a wide growth area.
In Patent Literature 2, coping with an issue to prevent occurrence of replant failures, technology is disclosed, which prevents replant failures by energizing between positive and negative electric terminals by burying the two electric terminals in both sides of cultivation soil. According to the technology mentioned in the Patent Literature 2, applying a weak DC current between the two electric terminals decomposes and ionizes inorganic salts that exist in soil and inhibit plant growth, but the inorganic salts ionized to positive ions and negative ions are accumulated in the vicinity of the each electric terminal. And, the accumulated inorganic salts are to be removed respectively.
The technology mentioned in the Patent Literature 2 is the technology, which applies a DC current between the positive terminal and the negative terminal in the cultivation soil, and thus the effect of applying a DC current is limited to a narrow area between the positive and negative terminals. Furthermore, if one-directional DC current was applied between two electric terminals for several months, the terminals corroded due to electric corrosion that is a kind of electrolysis, and it would be probable that replacement of the electric terminals becomes necessary. Therefore, an issue exists that it is difficult to continuously apply to a wide plant growth area.
In Patent Literature 3, technology is disclosed, in which pots are electrically insulated from the ground by insulation sheets, one electric terminals are buried in the vicinity of plants planted in the pots, the other electric terminals are buried in the ground close to the pots, and high voltage is applied to the plants from the electric terminals buried in the pots. According to the technology in the Patent Literature 3, electric current is applied indeterminately either a DC current or an AC current. However, in the case of a high-voltage AC current, ozone emits from the positive electric terminals, which is hazardous to instruments or plants, thus an issue exists that the plants in the pots cannot be raised.
In Patent Literature 4, technology is disclosed, which accelerates plant growth by irradiating minus ions towards plants cultivated in a seedbed, etc. The technology mentioned in the Patent Literature 4 adopts needle electric terminals for negative electric terminals and conductive resin with plural openings for positive electric terminals, and projects an extremely weak corona discharge from the negative electric terminals towards the positive electric terminals. With this, a large amount of minus ions can be produced without emitting ozone that is hazardous to instruments and inhibit plant growth.
However, the technology mentioned in the Patent Literature 4 needs to have an apparatus that can change the distance between the plants and the minus-ion modules that produce minus ions. Since it is difficult to arrange minus-ion modules so as to cover a wide plant growth area entirely, there is an issue that the technology cannot be applied to a wide plant growth area.
In Patent Literature 5, the technology to accelerate growth of plants planted in the soil of planters electrically insulated from the ground is disclosed. The technology mentioned in the Patent Literature 5 applies negative DC voltage to the plants by burying negative electric terminals in the soil of the planters so that the negative DC voltage applied by the negative electric terminals does not spread to the ground. With this, it is claimed that the negative DC voltage can be applied intensively to the plants.
In the technology mentioned in the Patent Literature 5, AC voltage is boosted and converted to DC voltage by a rectifier circuit. When converted to the DC voltage, a sine-wave waveform of the AC voltage is leveled and the boosted AC voltage is smoothened. Therefore, in order to gain certain high DC voltage after rectification, it is necessary to boost the high voltage before rectification to higher voltage than the voltage after rectification. There is an issue that the technology is inefficient and difficult to apply to a wide plant growth area, since a power loss occurs at the rectification.
In Patent Literature 6, the technology is disclosed, which improves soil environment by radiating electrons produced by an electron generation device to the soil. According to the technology mentioned in the Patent Literature 6, it is claimed that radiating electrons to the soil decreases colon bacilli, etc. that inhibit plant growth, as well as increases aerobic bacteria that accelerate plant growth.
However, it is difficult to exert the effect of electrons efficiently to a wide-range plant growth area by the bar-shaped electron-radiating parts mentioned in the Patent Literature 6, and providing a technology of plant growth acceleration system, which can radiate electrons efficiently to a wide range, was a problem.